Method and corresponding system for spectrum management

ABSTRACT

Method and corresponding system for spectrum management featuring advanced frequency-allocation planning and advanced interference avoidance. The invention discloses access points that transmit directionally and assigning a predefined channel in a predefined direction, in order to reduce interference between closely located access-points

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to wireless communication systems and,more particularly, to method and corresponding system for spectrummanagement featuring advanced frequency-allocation planning and advancedinterference avoidance.

Prior art solutions enable the placement of wireless Access Points (APs)in close proximity by reducing their transmission power. However,reducing the transmission power reduces the QoS and/or performanceprovided by the WLAN and, in some cases, even does not significantlyenlarge the number of users served.

SUMMARY OF THE INVENTION

The present invention relates to wireless communication systems and,more particularly, to method and corresponding system for spectrummanagement featuring advanced frequency-allocation planning and advancedinterference avoidance.

The present invention for method and corresponding system for spectrummanagement successfully address limitations of presently availabledevices and methods for wireless communication.

Implementation of the method and corresponding system for spectrummanagement of the present invention involves performing or completingselected tasks or steps manually, semi-automatically, fullyautomatically, and/or, a combination thereof. Moreover, according toactual instrumentation and/or equipment used for implementing aparticular preferred embodiment of the disclosed method andcorresponding system, several selected steps of the present inventioncould be performed by hardware, by software on any operating system ofany firmware, or a combination thereof. In particular, regardinghardware, selected steps of the invention could be performed by acomputerized network, a computer, a computer chip, an electroniccircuit, hard-wired circuitry, or a combination thereof, involving aplurality of digital and/or analog, electrical and/or electronic,components, operations, and protocols. Additionally, or alternatively,regarding software, selected steps of the invention could be performedby a data processor, such as a computing platform, executing a pluralityof computer program types of software instructions or protocols usingany suitable computer operating system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedfor the purpose of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the present invention. In this regard, no attempt is made to showstructural details of the present invention in more detail than isnecessary for a fundamental understanding of the invention. Moreover,the description taken with the drawings makes apparent to those skilledin the art how the several forms of the invention may be embodied inpractice. Identical structures, elements or parts which appear in morethan one figure preferably are labeled with a same or similar number inall the figures in which they appear. In the drawings:

FIG. 1 is an illustration of an exemplary architecture in accordancewith the present invention;

FIG. 2 is an illustration of an exemplary embodiment of an AP inaccordance with the present invention;

FIG. 3 is an illustration of a wireless network architecture inaccordance with the present invention;

FIG. 4 is an illustration of another wireless network architecture inaccordance with the present invention;

FIG. 5 is an illustration of a wireless network with Radius inaccordance with the present invention;

FIG. 6 is an illustration of stand alone APs in accordance with thepresent invention; and

FIG. 7 is an illustration of stand-alone APs with local accesscontroller in accordance with the present invention.

FIG. 8 is an illustration of a generalized IEEE 802.11 type of protocolin accordance with the present invention,

FIG. 9 is an illustration of a spectrum-management algorithm that isrunning in a distributed manner in accordance with the presentinvention,

FIG. 10 is an illustration of an exemplary channel allocation plan thatin accordance with the present invention,

FIG. 11 is an illustration of two APs, that cover the same stations,

FIG. 12 is an illustration of a transmit power control in accordancewith the present invention,

FIG. 13 is an illustration of a directional transmit power control inaccordance with the present invention,

FIG. 14 is an illustration of load balancing in accordance with thepresent invention,

FIG. 15 is another illustration of load balancing in accordance with thepresent invention,

FIG. 16 is still another illustration of load balancing in accordancewith the present invention,

FIG. 17 is an illustration of the QoS as a function of the number ofsimultaneous sessions in accordance with the present invention, and

FIG. 18 is an illustration of a channel monitor in accordance with thepresent invention.

DETAILED DESCRIPTION

The present invention relates to wireless communication systems and,more particularly, to method and corresponding system for spectrummanagement featuring advanced frequency-allocation planning and advancedinterference avoidance.

The present invention is method and corresponding system for spectrummanagement. The preferred embodiments of the present invention arediscussed in detail below. It is to be understood that the presentinvention is not limited in its application to the details of the orderor sequence of steps of operation or implementation of the method setforth in the following description, drawings, or examples. Whilespecific steps, configurations and arrangements are discussed, it is tobe understood that this is done for illustrative purposes only. A personskilled in the relevant art will recognize that other steps,configurations and arrangements can be used without departing from thespirit and scope of the present invention.

Herein, the terms “relevant zone of interest” or “zone of interest” or“area of interest” refer to the zone containing all stations, also knownas users, and Access Points (APs) that affect the performance of arelevant AP. Without limiting the scope of the present invention, therelevant AP is, in most cases, the AP that the methods of the presentinvention are applied to. Moreover, the relevant zone of interestincludes the stations and APs from which the relevant AP receivestransmissions, and stations and APs that influence the performance ofthe relevant AP.

Hereinafter, the term “jitter” refers to the variation of the delay ofpacket transmission. The jitter is calculated in relation to the timeswhen stations would like to transmit the packets. For example, when astation wants to transmit packets every 20 mili-seconds, but succeeds intransmitting packets only every 24 mili-seconds, there is a jitter of 4mili-seconds.

Hereinafter, the term “streaming data” refers to data that is structuredand processed in a continuous flow, such as, without limiting the scopeof the present invention, digital audio and video, and preferably Voiceover Internet Protocol (VoIP) and Video over Internet Protocol.

Hereinafter, the term “IEEE 802.11 type of protocol” refers to anywireless standard under IEEE 802.11, including but not limited to,802.11b/ g/ a/ e/ i/ k/ r/ v/ s/ n/ u/ y/ w

Referring now to the drawings, FIG. 1 illustrates an optionalarchitecture of a preferred embodiment of the present invention.Referring to FIG. 1, there is at least one Multi-Access Point (MAP).Each MAP (referred to as 11A, 11B, 11C, or 11) represents at least twoAPs (12A, 12B, and 12C) that are controlled by the same manager; themanager may be located at local management 13 and/or global management17. Optionally, each MAP may, in addition, feature a bridging 14 deviceand/or local management 13. For the sake of simplicity, FIG. 1 does notreflect that MAPs 11B and 11C include the same abovementioned devicesshown in MAP 11A.

MAP 11 sends and receives data to and from network 25. Network 25 may bea standard network. Optionally, MAP 11 communicates with globalmanagement 17 algorithms and Network Management System (NMS) 18. Thosecommunications may be operated by a local/global protocol and aglobal/local protocol.

FIG. 1 illustrates MAP 11A featuring three APs referred to as 12A, 12B,and 12C. Local management 13 manages at least two Access Points (APs) 12as disclosed herein. Access Points (APs) 12A-C, may be located close toone another and may operate either simultaneously or independently.Preferably, each AP transmits on a different channel. Optionally, an APis able to transmit on more than one channel.

Local management 13 is responsible for Load-Balancing (LB) the channels“owned” by MAP 11A, and for local optimization of theSpectrum-Management (SM). Local management 13 uses a set of algorithms,referred to as local management algorithms. Local management algorithmsevaluate the state of each channel and the state of each station, andoptimize the network in order to provide the required performance.

At least two APs 12 are able to operate simultaneously, and in closeproximity, thereby introducing design requirements for channelisolation. This ability of AP/APs to simultaneously operate alsointroduces operational capabilities of spectrum management and loadbalancing.

It is to be understood that the location of global management algorithms17 and Network Management System (NMS) 18 and their way ofimplementation exemplifies only one embodiment of a device featuring atleast two channels, in accordance with the present invention. In actualoperations and/or in other equivalent embodiments, global management 17algorithms and Network Management System (NMS) 18 may have otherembodiments. However, it is to be understood that these are onlyexamples of the present invention, and there is no intent of limitingthe scope of the present invention to the specifically disclosed globalmanagement algorithms, and/or Network Management System (NMS), and/orIEEE 802.11 type of protocol.

Moreover, in an exemplary embodiment of the present invention, thesessions are voice over IP (VoIP) sessions, and/or multimedia over IPsessions. It is to be understood that VoIP is only an example of astreaming application for which the present invention is useful. For thesake of simplicity, the disclosure of the present invention isillustrated using both references and examples mostly related to VoIPapplications. However, it is to be understood that these are onlyexamples of the present invention, and there is no intent of limitingthe scope of the present invention to VoIP applications and/or toMultimedia over IP applications. Moreover, some of the algorithms of thepresent invention may be executed on OSI Layer Two (frames), OSI LayerThree (packets), or any other appropriate layer. It is to be understoodthat any reference to packet or frame is for illustrative purposes only,and a person who has ordinary skill in the area of the technology shouldbe able to convert between the two.

Steps, components, and operation of preferred embodiments of the methodsand corresponding devices of the present invention are further describedherein. Referring back to the drawings, FIG. 2 is a block diagramexample illustrating an embodiment of AP 12 in accordance with thepresent invention, constructed and functional for operating at least twochannels. Alternatively, each channel may be operated by a different AP.AP 12 features components: (a) smart antenna 36, (b) optional channelfilter 35, (c) transceiver 34, (d) optional beamformer 33 operatingsmart antenna 36, (e) Modem 30, and (f) optional CPU 37.

Modem 30 may be a commercial off-the-shelf modem. Because it may not bepossible to modify a commercial off-the-shelf modem, all the proprietaryalgorithms may be implemented in CPU 37, which is connected to MAC 31.Althernatively, CPU 37 may be connected to other parts of modem 30.

Hereinafter the term “smart antenna” refers to a smart antenna, and/oradaptive antenna, and/or an antenna array featuring at least tworadiating elements. In reference to FIG. 2, the smart antenna is antenna36. Compared to an omni-directional antenna, smart antenna 36 focusesthe transmission and receives only from a certain direction, whileintroducing, amongst others, the following benefits: extended range,high availability of bandwidth per user, and reduced effect ofinterference. Moreover, by using smart antenna 36, the system of thepresent invention may implement beamforming and/or transmit diversitytechniques, as known in the art. Alternatively, some parts of thepresent invention may be implemented without using a smart antenna.

Additional objects, advantages, and novel features of the presentinvention will become apparent to one of ordinary skill in the art, uponexamination of the following possible embodiments, which together withall other descriptions illustrate the present invention in anon-limiting fashion.

In one embodiment of the present invention, each AP controls its ownsmart antenna and there is no real time connection between the differentAPs within MAP 11A. Optionally, the connection between the APs islimited to load balancing and spectrum management. According to thisoptional embodiment, the load balancing algorithms and spectrummanagement algorithms control and manage the distribution of thewireless resources. Additionally, or alternatively, in anotherembodiment of the present invention, global management 17 algorithms setlocal management 13 policies and may allocate stations to APs.

Referring now back to the drawings, FIG. 3 to FIG. 7 illustrate optionalconfigurations of the system of the present invention. It is to beunderstood that these are only examples of the present invention, andthere is no intent of limiting the scope of the present invention to thespecifically disclosed configurations.

FIG. 3 illustrates a system, wherein an access controller, whichincludes a Network Management System (NMS), might also collect packetinformation and classify it, as well as features the Service LevelAgreement (SLA) and profile of the user.

FIG. 4 illustrates an embodiment where there is no traffic through theNetwork Management System and all packet manipulation is performed inthe AP.

FIG. 5 illustrates an embodiment with Radius, where there is no trafficthrough the Network Management System but it features the SLA andprofile of the user, which might influence the load balancing andspectrum management algorithms.

FIG. 6 illustrates a stand alone AP, where there is no NetworkManagement System at all, and all spectrum management and load balancingshould be done locally at the AP.

FIG. 7 illustrates a stand-alone access point with local accesscontroller and Network Management System.

Load Balancing

According to an aspect of the present invention, the stations are loadbalanced between at least two channels. When a station is load balanced,the station is disconnected or moved. When a station is moved, it can bemoved either to another channel of the same AP, or to another AP, or toa specific channel of another AP.

Referring now to the LB algorithms, LB algorithms manage at least twosimultaneously-operated channels in order to maximize the channels'efficiency. The LB algorithms ensure that the wireless resources arebeing used in an optimum way so that stations receive the requiredservice. Channel LB is performed by at least one of the following:

(a) Changing RF parameters.

(b) Moving stations from one channel to another channel.

(c) Moving stations from one AP to another AP. For example, moving astation from MAP 11A to MAP 11B.

(d) Moving a station to another AP on the same channel.

(e) Not accepting a station if the station does not match a predefinedcriterion such as being located in a predefined direction.

[Required AP Characteristics]

An AP of the present invention is able to cause stations to move betweenchannels and APs according to a LB decision.

Exemplary methods for moving stations between channels and APs are: (a)Using a standard that has a moving command. (b) Sending a station adisassociation or disauthentication message. (c) Controlling signalspower in order to cause a station to change its channel/AP.

Preferably, an AP is able to calculate the Direction of Arrival (DOA) ofa received signal, and/or the location of the station from which thesignal is received, and/or the distance of the stations from the AP.

DOA, location, and/or distance of the received signal may be calculatedby using known in the art methods such as:

Using a directional antenna.

Receiving signals from more than one antenna element and calculating thedirection of a station using the information from all received signals.

Using time synchronization measurements from at least two APs.

Reading the location of a station using a GPS on the station or anyother equivalent location mechanism.

Using RSSI for calculating the distance.

The DOA may change because of the path between the station and the AP,in which case the DOA of the received signal is not the true DOA of thetransmitting station. Therefore, it is advantageous to use anappropriate algorithm that uses information from more than one AP andcompensates for the multipath error.

Creating an information table that holds information about each stationand, optionally, the power with which transmissions from that stationare received by other relevant stations and/or APs.

For example, the information table may be a received power tableindicating which stations receive what stations, at what power andoptionally from which direction.

The LB creates an information table which estimates the location ofpredefined stations in relation to the location of predefined APs.Alternatively or additionally, the information table indicates whichstation receives what stations. The information table is created byusing the ability of the APs to calculate the DOA and RSSI of receivedsignals and to know from which station the signals were transmitted.Optionally, the received power table is calculated according to thefollowing steps:

(a) Receiving transmissions from predefined stations in a predefinedarea.

(b) Extracting the distance and the direction of the received stations.Optionally, the directions to the received stations are calculated byusing one or more of the following optional methods:

Using a directional antenna,

Optionally, data about each station is collected from more than one APand calculating the location of a station is performed by using datafrom more than one AP. Optionally, data from all APs receiving a stationis processed in order to improve the station's location estimation. Thisis highly useful for overcoming the multi-path effect.

Optionally, the distance of a station is estimated by the receivedtransmission power.

Optionally, the system extracts and/or calculates a station's locationby receiving information received from the station itself.

According to an alternative option, when communicating with stationsoperating in two networks, such as dual mode stations or dual bandstations or handsets, it is possible to receive information about thelocation of the dual mode station from the second network. For example,cellular GSM provides location information. Optionally, 802.11k standardmay be used to receive measurements for building the information table.Optionally, GPS information received from the station may be used forcalculating the relative location of the station.

Optionally, the system is updating the information table.

The information table is updated and its precision is enhanced bychecking various parameters and at least one of the following exemplarydynamic effects that may indicate that the information table should beupdated.

A station is moving,

Transmission blocking/main transmission path changes, for example,because of a moving object, or

Measurement error.

In an embodiment of the present invention, the LB is based on measuringthe number of retransmissions of stations.

Optionally, the LB, and especially the step of allocating stations togroups, takes into account the RSSI and the overall channel utilization.By using these measurements, it is possible to locate the station thatcauses the problem and to move it to another channel/AP or disconnectit. In this case, reasons for estimation mistakes may be wrongDOA/location estimation and/or wrong estimation of receiving sensitivityor transmit power. In order to further improve the LB, the following arealso used:

RSSI and DOA as received on other APs (on the under investigationstation) are also used.

Information received from the station itself. Information from thestation itself may be collected by implementing standards, such as IEEE802.11k, that supply such features. Alternatively, proprietary protocolsfor collecting information from the station itself may be implemented.

Allocating the same channel to closely located stations by usingdirectional information:

In an embodiment of the present invention, AP 12 is able to assign thesame channel to closely located stations by using DOA information.Alternatively, AP 12 is able to assign the same channel to closelylocated stations by using information about the stations' location.Optionally, AP 12 is able to assign the same channel to closely locatedstations by using DOA information and information about the stationslocation.

By assigning the same channel to closely located stations, AP 12 assuresthat all, or most, of those stations receive one another; and thus, theamount of collisions is reduced.

Referring to FIG. 16, all stations in Group 1, referred to as 200, usethe same channel. Stations in Group 2, referred to as 201, may use thesame channel used by Group 1, but preferably, Group 2 stations useanother channel or channels.

In order to reduce the number of hidden stations and collisions, and toincrease performance, a main object of the present invention is toseparate between stations which do not receive each other and arereceived by one or more APs. Referring to FIG. 14, when two stationsthat communicate with the same corresponding AP do not receive eachother while their corresponding AP receives them both, the two stationsshould be assigned to different channels of the AP. Referring to FIG.15, in the case where there are at least two APs and their correspondingstations, wherein the stations do not receive each other but the APsreceive the stations—the stations should be assigned to differentchannels. For example, when two stations are both received by two APsand the stations do not receive each other, the stations should beassigned to different channels.

Using a smart antenna changes the hidden stations phenomena. Themanaging algorithm that calculates which station receives what stationand decides how to move a station, has to take the hidden stationsphenomena into account. For example, when there are two hidden stationsfrom opposite sides of an AP, such that station A does not receivestation B and therefore both of them transmit in the same channel, thenusing an AP having a normal omnidirectional antenna results in acollision (classical hidden station). But when using an AP having asmart antenna, the AP may direct its beam to receive the signal fromstation A and not to receive station B's transmissions, and thus thereis no collision.

Improving LB performance by detecting moving stations and moving thestation before the system performance degrades.

The ability to estimate a station's location, enables the presentinvention to estimate whether the station is portable or not, accordingto the changes, as a function of time, of its reception angle and/orpower. Knowing the direction in space in which the station is movingenables the present invention to plan to which AP/channel the station isto be connected, ahead of time. This planning ahead of time enables thesystem to perform better LB between channels and stations. Moreover,planning ahead of time enables the present invention to have bettersystem performance. A main benefit is that the network is able to movethe station to another channel before that station degrades theperformance of the network, rather than after a performance degradationis measured. Moreover, this method maintains the system at a higherlevel of total performance, and increases system stability and QoS.

According to another aspect of the present invention, the performance ofa wireless network is improved by using a directional antenna operationas disclosed below.

The present invention solves problems related to the use of directionalantennas, which are known to introduce problems, such as hidden stationsand deaf stations. On the one hand, using a directional antenna providesthe ability to focus on providing higher quality transmissions withfewer disturbances to a specific station. On the other hand, a stationoutside the beam cannot receive the transmission, and therefore assumesit is allowed to begin a transmission. Moreover, an optional wirelesssystem having a directional antenna does not receive transmissions froma station outside the beam, resulting in transmission failure for thestation. In summary, using a directional antenna improves theperformance for a specific station, but at the same time, causesproblems for the remaining stations located outside the beam. Thestations that are located outside the beam expect the AP to transmitomnidirectionally, and therefore, if they are not receiving atransmission, the stations assume the AP is not transmitting, andtherefore incorrectly assume that they may transmit.

An optional solution to the above hidden and/or deaf station problem foran IEEE 802.11 type of protocol is transmitting a ‘Clear To Send’signal, referred to hereinafter as CTS. In an exemplary embodiment ofthe present invention, a smart antenna is used for directionaltransmissions. Directional transmissions may be either beamforming ortransmit diversity. For the sake of simplicity, the disclosure of thepresent invention is illustrated using both references and examplesmostly related to CTS and RTS-CTS. However, it is to be understood thatthese are only examples of the protection mechanism of the presentinvention, and there is no intent of limiting the scope of the presentinvention to CTS and RTS-CTS. Whenever the AP requests permission totransmit, it transmits a CTS. When a station receives the CTS, it knowsit is forbidden from transmitting at this time. The CTS is transmittedusing an omnidirectional transmission so that all stations receive theCTS signal, and refrain from transmitting for a predetermined amount oftime. This solution is suitable only for the range of omnidirectionaltransmissions. In the extended range, beyond the range of theomnidirectional transmission, the CTS is transmitted by directional RTS(request to send). Optionally, a directional RTS is used as a protectionmechanism.

Prior art uses CTS and RTS for other uses. Originally, CTS was used forcombining IEEE 802.11b and IEEE 802.11g stations. RTS and CTS areusually used for large packets. The IEEE 802.11g standard uses theRTS-CTS and the CTS-to-self mechanisms in order to protect thetransmissions of an IEEE 802.11g standard from IEEE 802.11b stationsthat cannot decode the IEEE 802.11g transmissions. Moreover, dependingon the location of the stations in a network, another option is to useomnidirectional CTS for commanding the stations not to transmit.

The above-described mechanisms were created in the IEEE 802.11 type ofprotocol to resolve problems with problematic channels. The standardmakes it possible to transmit an RTS signal and/or receive a CTS signal,and only then to send the information. This is instead of sending alldata right from the start, without having any indication whether theother side is receiving the transmission or not.

The decision when to transmit omnidirectionally and when to transmitdirectionally takes into account at least one of the followingparameters:

Location of the station.

Received RSSI (Received Signal Strength Indicator).

Rate of transmission.

The implemented standard.

The solution to the hidden and deaf station problem takes into accountthe advantages of using directional antennas transmissions, versus thedisadvantages that result from the need to use preventive steps, such asRTS-CTS, in the hidden and deaf stations. Moreover, the solution maydetermine the best mixture point that sets how beneficial it is totransmit directionally, and how beneficial it is to transmitomnidirectionally.

An improved optimization may be reached when the location of thestations is known. When the location of the stations is known thealgorithm can take into account which station receives what station, andbased on that decide when to use directional transmission and when touse omnidirectional transmission.

The transmission angle resulting from using beamforming is wider thanthe transmission angle resulting from using transmit diversity.Moreover, beamforming is more resistant to changes in thecharacteristics of the channel and to movements of stations whencompared to transmit diversity. On the other hand, transmit diversityfeatures a higher transmission range and an improved rate.

When using beamforming or transmit diversity, there is an extended rangethat cannot be reached by omnidirectional transmission. In an exemplaryembodiment of the present invention, beacons and broadcast are used withbeamforming implementation for obtaining an extended range. Therefore,broadcast is transmitted by omnidirectional transmission and extendedranges are covered by directional transmissions.

Optionally, the directional transmissions are scheduled according to aspanning plan or a predefined order having specific and fixed timecharacteristics.

In an embodiment of the present invention, the following LB method isused to ensure a predefined performance level for selected stations, forexample, a minimum amount of Mbit/sec for each station.

The LB is distributing stations between at least two channels accordingto predefined parameters, such as RSSI and DOA.

The bandwidth of active stations is measured repeatedly.

If an active station does not receive the ensured performance on aspecific channel, the station is moved to another channel or to anotherAP.

The LB selects the station to be moved according to the predefinedparameters. By moving the station, the system ensures that thepredefined stations receive the predefined performance. As long as thepredefined stations do not receive the predefined performance, stationsare moved between channels and/or APs in order to obtain a situationwherein the predefined stations receive the predefined performance.

By using the novel LB method of moving active stations between channelsand/or APs, it is possible to exploit the channels better and moreefficiently.

Spectrum Management

According to another aspect of the present invention, interference isreduced by using the following spectrum-management (SM) method andcorresponding device.

Implementing the spectrum-management of the present invention results inat least one of the following significant benefits:

(a) Improving wireless network coverage and performance.

(b) Handling the relationships between different APs. For example,enhancing performance by allocating power, frequency and beam shapesaccording to locations of APs, locations of stations, path loss,interference, etc.

(c) Canceling interference by forming nulls on disturbing angles. It isto be noted that almost any interference can be canceled by placingnulls. If the interference is WLAN interference—the interference may beresolved by using LB. If the interference is non-WLAN interference—theinterference may be resolved by placing a null in the interferencedirection.

(d) Changing the beam shape in order for the WLAN to meet therequirements of a scenario. This is in contrast to prior art APs that donot feature beamforming and especially do not have feature dynamicbeamforming.

Referring to FIG. 8, which illustrates a generalized IEEE 802.11 type ofprotocol in accordance with the present invention, each of MAPs 11A, 11Band 11C, represents at least two channels that are controlled by thesame manager; the manager may be located at local management 13 and/orglobal management 17. In the case where a spectrum-management algorithmis run in global management 17, global management 17 builds a map thatstores the locations of available stations and APs. Global management 17uses the locations map and the instantaneous performance of the networkto assign the channels, beam shapes, and distribute the stations betweenthe available APs and channels in order to minimize the interference(including internal interference). For example, if a global management17 algorithm finds that the best performing channel is not assigned toeither the fastest stations and/or stations having the highest priority,then global management 17 reassigns that channel to the fastest/highestpriority stations.

Optionally, the channels assignment algorithm is re-executed on anongoing basis, and for all areas and directions.

The wireless network of the present invention may feature differenttypes of APs (single-channel and multi-channel) and a centralspectrum-management system receiving relevant information from the APs.

According to an additional exemplary architecture, local management 13is located in global management 17. That case, the spectrum-managementalgorithm can be run distributed or centralized. FIG. 9, illustrates aspectrum-management algorithm that is running in a distributed manner.APs 160, 162, and 164, each run a spectrum-management module, where theSMs are connected to one another and each spectrum-management module isresponsible for communicating with other spectrum-management modules itinterferes with.

In an embodiment of the present invention, the spectrum-managementalgorithm implements an advanced frequency-assignment planning.

The advanced frequency-assignment planning deals with using specificfrequencies in certain areas, to reduce the mutual interference betweenclosely located APs. The advanced frequency-assignment planning can beimplemented when at least two APs are operated under the same SM. Theadvanced frequency-assignment planning is made possible by using a smartantenna, which enables the present invention to transmit within narrowangles. Moreover, in an embodiment of the present invention, each AP hasat least two channels and has the ability to place nulls.

FIG. 10 illustrates an exemplary channel allocation plan that preventstwo or more APs (130 and 132) from covering an overlapping area with thesame frequency. As illustrated by FIG. 10, APs (130 and 132) have 3channels (150-155) each. AP 132 transmits in channel #3 155 towards AP130, and AP 130 transmits in channel #2 152 towards AP 132.

By using transmit power control, DOA information, and optionallydirectional transmission, the wireless network can make sure that itaccepts users only from the required channel and direction, according tothe APs' channel coverage map, as illustrated in FIG. 10. Moreover, thenetwork is able to limit the APs transmissions according to the map, anduse LB mechanisms for spectrum-management usage and performanceenhancement.

In another embodiment of the present invention, the spectrum-managementalgorithm implements an advanced interference avoidance planning.

The advanced interference avoidance planning handles interferencearriving from a known direction by using a smart antenna, which enablesthe system to place at least one narrow-angle null in the knowninterference direction.

Referring to FIG. 8, in order to reduce or prevent interference betweendifferent APs and/or to prevent overloading a selected frequency withtoo many stations, the sectors referred to as Beam #1 and Beam #2 usedifferent frequencies. This directional spectrum-management reducesinterference in areas covered by two or more APs. Optionally, null 1 isplaced in the estimated direction of a closely located AP. Null 1 may bedirected to to MAP 11B and/or to areas with a plurality of stationsassociated to other APs on the same channel.

In an embodiment of the present invention, the spectrum-managementalgorithm is a dynamic algorithm.

The dynamic spectrum-management algorithm maps both the stationsexperiencing interference and the direction of the interference. Aftercompleting the interference mapping, the channels are dynamicallyassigned to the stations such that channels experiencing higherinterference are assigned to stations featuring lower rates.

The dynamic spectrum-management algorithm accomplishes at least one ofthe following:

(a) Improving the spectrum-management algorithm.

(b) Improving the LB algorithm.

(c) Improving frequency distribution across channels and directions, and

(d) Improving the estimation regarding which areas are heavily-loadedwith stations.

Optionally, the aforementioned dynamic feature is used for demonstratingto an operator the location of the loaded areas and their deployment.Optionally, the spectrum-management dynamically collects and storesinformation about the network, which it uses for further improvements.

The ability to control transmission power is known in the art, but theability to distribute the stations between at least two channelssimultaneously, according to the stations' characteristics, is a noveladvantage of the present invention. In an embodiment of the presentinvention, the wireless network transmits using low power to closelylocated stations and receives with a high receiving threshold.Optionally, the channels that are near the transmitting AP (usually thefastest channel) transmit with the lowest power. At the same time,high-power transmission is used over another channel, to far-awaystations.

In an embodiment of the present invention, an IEEE 802.11 type ofprotocol, which does not support power control, is implemented. In thiscase, the distance to the station is approximated by measuring power andangle.

In still another embodiment of the present invention, the system createsa transmission pattern featuring a required shape needed forimplementing the spectrum-management algorithm. The transmission patternmay constantly have the required shape or have the required shape onlywhen transmitting beacons. Setting the transmission pattern to have therequired shape only when transmitting beacons causes the receivingstations to receive the transmitting AP according to the transmissionshape. Three optional embodiments for setting the transmission patternto have a required shape are:

(a) Transmitting with an antenna featuring the required transmissionpattern.

(b) Dividing the transmission area into sectors and transmitting aspecific beacon, featuring the right power, to each sector. Using thisbeacon customization makes it possible to create the required shape. Itis noted that not transmitting the same signal to all directions is aparticular case of this embodiment.

(c) The AP transmits in all directions, but responds only to Probesignals and/or association signals from stations that it wants to add toa specific channel. More specifically, the AP responds to a problemand/or to an association request related to stations featuring directionof arrival and RSSI as required and ignores all other stations.

Spectrum-management may implement dynamic null as follows.

Optionally, the spectrum-management algorithm of the present inventionplaces at least one dynamic null, as disclosed herein. When there is anoverlapping area between APs, transmission from stations in that areamay be received by the overlapping APs, and these APs may receive thestations' probes. Taking into consideration the fact that stations'probes are sent to Network Management System 18 from more than one AP,together with the probes' DOA, Network Management System 18 is able tocalculate the overlapping area of those APs. Optionally, NetworkManagement System 18 bases its overlapping calculations on more than onestation's statistics. After extracting the overlapping area of thoseAPs, the Network Management System is able to place dynamic nulls in thedirection of those overlapping areas, thus decreasing the interferencesbetween the APs.

It is to be understood that nulls may be used for dealing with generalinterference and are not solely restricted to overlapping problems.

Spectrum-management may implement a transmit power control as follows.

Transmissions by at least two different APs interfere with one anotherwhen each receives the other's transmissions. By means of optimization,which reduces the transmission power in different directions, it ispossible to bring the APs into closer proximity with one another, whilestill restricting their mutual interference to an acceptable level. Theability to control the mutual interference holds great value, especiallyin places where the number of stations per square meter is large.Whenever there is a large number of stations per square meter, there isa need to bring the APs closer to each other in order to handle allstations. Prior art solutions enable the placement of APs in closeproximity by reducing their transmission power. However, reducing thetransmission power reduces the QoS/performance provided by the WLAN,and, in some cases, even does not significantly enlarge the number ofstations served.

By implementing transmit power control, the system of the presentinvention is able to transmit at a variety of powers to differentdirections. As a result, a station may receive transmissions from onlyone AP, even if it is located in an area which, in principle, is coveredby at least two different APs. Referring now back to the figures, FIG.11 illustrates two APs, 102, and 103, that cover the same stations 100.In this case, stations 100 receive transmissions from both APs. FIG. 12illustrates a transmit power control in accordance with the presentinvention, wherein each station 100 receives transmission only from AP102 or AP 103. FIG. 13 illustrates a directional transmit power controlin accordance with the present invention, wherein each station 100receives transmission only from AP 102 or AP 103.

As illustrated in FIG. 12 and FIG. 13, since an AP features adirectional antenna having gain, it is possible for the AP to receiveanother nearby AP, which, due to the transmit power control, does notinterfere with the stations and therefore does not transmit. In order toprevent long time-intervals in which an AP is not transmitting becauseit receives a nearby AP, it is advantageous for the AP to have areceiving threshold as high as possible, that causes the AP to ignoreother transmissions with power that is lower than a predefined number ofdecibels. Ignoring the other transmissions having power that is lowerthan a predefined number of decibels, enables the AP to transmit.

Increasing the receiving threshold of the AP may contradict somestandards, especially the IEEE 802.11 type of protocol, which requires areasonable threshold of reception. A reasonable threshold of receptionis required because it is undesirable for a system to transmit before ittries to sniff the medium, and check if other systems are transmittingat the same time and on the same frequency. In an embodiment of thepresent invention, the system features a receiving threshold that islower than the receiving threshold required by the standard. In such acase, the system is able to control its receiving threshold, and toincrease the receiving threshold to the maximum allowed by the standardin specific cases.

Maximum Number of Sessions Restriction

According to another aspect of the present invention, the maximum numberof session in an IEEE 802.11 type of protocol is limited in order toprevent saturation. The maximum number of sessions restriction mechanismof the present invention maintains QoS of wireless networks bydynamically calculating a maximum number of streaming sessions andensuring that this maximum number of streaming sessions is not exceeded.Prior art WLAN does not control the number of sessions, so when themaximum number of simultaneous sessions is reached, the QoS for allstations is reduced drastically. The ability to control the number ofsessions is a novel advantage of the present invention.

The session restriction mechanism of the present invention may beoperated in any known in the art network architecture, such as, but notlimited to, the following network architectures.

(a) One AP that communicates with a plurality of stations through onechannel. (b) One AP that communicates with a plurality of stationsthrough at least two channels. In this case, the various stations aredistributed between the available channels. (c) Communication networkcontrolled by a global SM and/or global LB mechanism. The global SMand/or global LB mechanisms are able to move stations between theavailable APs. Optionally, the global SM and/or global LB algorithm maybe a distributed algorithm executed on the APs or on another hardwareplatform.

High QoS is received by all stations in the network until a streamingsaturation point is reached, as illustrated in FIG. 17 by reference 100.Whenever the wireless network exceeds streaming saturation point 100,the QoS for all stations is reduced drastically.

It is to be understood that the location of streaming saturation point100 depends on the stations communicating with the current AP and alsoon the interference by other stations. The other stations maycommunicate with a nearby AP or any other type of device transmitting onthe relevant frequencies. Therefore, the graph illustrated in FIG. 17 isderived from the overall system performance.

The network may reach point 100 when at least one of the conditionsdescribed below occur. The novel session restriction algorithm of thepresent invention may be operated on the downlink channel and/or on theuplink channel. The reasons for reaching saturation point 100 on theuplink and downlink channels are usually similar. Moreover, theparameters used for the calculation are usually similar. The scenariosfor reaching saturation point 100 are usually different on the uplinkand downlink channels, and influence the measuring of parameters and thesolution. Usually there is no direct connection between the uplink anddownlink but in the case of WLAN using the same frequencies for uplinkand downlink channels, there is some correlation between the channelsand the channels may be likely to fall one after the other. Therefore,identifying a fall in one direction of a channel may be useful foridentifying a fall in the other direction of the channel as well.

The following examples illustrate events that may bring the wirelessnetwork to its saturation point 100.

A new station joins the network.

The environmental conditions change and/or external interference isadded. The external interference may be wireless LAN (WLAN) interferenceor non-WLAN interference.

The following examples disclose parameters that are useful forcalculating and measuring saturation point 100. At least some of thefollowing parameters, optionally with additional data, are used by thenovel maximum number of sessions restriction mechanism of the presentinvention.

The number of simultaneous streaming sessions in the network. Moreover,for each session, the system may monitor the type of the session andother relevant session properties, e.g., vocoder type, frame duration,and voice activity detection (VAD). As known in the relevant art,vocoder, also referred to as voice coder, is an electronicdevice/algorithm for synthesizing speech. A vocoder usually compressesthe voice and therefore changes the packet size. The vocoder may controlthe packets transmission time, and thereby may transmit bigger packetsin a lower frequency.

The transmission rates and number of retransmissions of the stationshaving streaming sessions.

The external interference of stations located in the area of interest ofthe network and other interference sources.

external non-WLAN interference.

Total performance of the wireless network.

The distribution/physical-location of the stations within the area ofinterest. It is to be noted that there are cases wherein a small changein stations distribution is enough to cause performance degradation, oreven a transmission path block.

Interference within data traffic that is transmitted at the same timefrom different stations or from the same AP or from different channelsin the same AP.

Rate control algorithm may influence saturation point 100. and

When using standard stations, the system of the present invention canonly control the AP operation. Therefore, for downlink, it is possibleto influence the rate control and various decisions regarding whatinformation to transmit, if any.

General Description of the Solution:

The method and corresponding system of the present invention has a highability to collect data from several OSI layers simultaneously. Theability to collect data from several OSI layers simultaneouslyfacilitates decision-making regarding load balancing and number ofsessions limitation.

In a preferred embodiment, the system counts the number of streamingdata stations, and is able to determine when the network is close toreaching its maximum capacity. Exceeding the system's maximum capacitycauses severe degradation in the QoS. By using the method for maximumcapacity calculation, optionally based on the disclosed parameters, thesystem is able to determine which stations are to be disconnected ormoved, according to the station's profile and/or station's performance.Moreover, in cases where the system exceeds maximum capacity, it ispossible to decide which station to keep and which station to move,disconnect or move to another channel, according to the station'sproperties. Examples of optional station profiles are VIP station, afrequent station, a visitor station, etc.

Referring again to FIG. 17, area 100 a between the origin and saturationpoint 100 may feature the following effects.

(a) Instantaneous degradation of QoS to one or more stations. Dependingon the characteristics of the instantaneous QoS degradation, the systemmy react or not take any action.

(b) Streaming data QoS degradation to some of the stations.

(c) At the end of area 100 a and before saturation point 100, there maybe a slight QoS degradation.

Optionally, WLAN QoS mechanisms are used in determining preference ofVoIP sessions, or other streaming sessions, over data transmissions onthe same channel. The following three examples disclose possible methodsfor determining the performance of the streaming sessions.

(a) Using WLAN QoS, such as 802.11e for QoS differentiation betweensessions, and QoS priority assignment between VoIP and other applicationand session types such as data session.

(b) Using WLAN QoS for separating between stations by assigningdifferent priority to different stations. This option is similar to themethod of differentiating between stations of different channels.

(c) In an optional embodiment, in order to supply a favorable service toVoIP sessions, synchronous QoS mechanisms, such as IEEE 802.11e-HCCA(polling), are used. The use of synchronous QoS mechanisms enables thesystem to systemically determine the working point in such a way thateach AP and/or area in the relevant zone of interest does not exceed thepoint represented by streaming saturation point 100. For example, byusing the methods disclosed in the present invention the capacity ofeach AP may be limited in order to enable other nearby AP or APs to workwell as well. Alternatively, there are at least two closely situatedAPs. Whenever at least two closely situated APs are operated without thepolling mechanism, each AP receives transmissions from the other APs andtakes them into consideration before starting to transmit, resulting innormal network operation. Operating the polling from a systemperspective is used in order to prevent each AP from attempting to fillthe channel completely, for example, with data transmissions that can bedelayed. Operating the polling from a system point of view results inallocating to each AP the greatest amount of resources that can beallocated without reaching streaming saturation point 100. Therefore,polling is a great solution for a single AP, but when operating highthroughput networks there is a need to synchronize all of the APs andlimit the performances of some/all of the APs in order to prevent caseswhere different APs interfere with one another, and as a result, networkperformance is reduced.

Steps, components, operation, and implementation of the method andcorresponding device for maximum number of sessions restriction,according to the present invention, are better understood with referenceto the following description and accompanying drawings.

QoS is maintained by an algorithm which calculates a dynamic maximumnumber of sessions and ensures that this dynamic maximum number ofsessions is not exceeded. The algorithm features the following steps:

Measuring network parameters. Network parameters may be measuredper-station and/or per-channel.

Examples of parameters measured per-station are: type of traffic (suchas data, VoIP, streaming video, and simultaneous multi-type station),rate, number of retransmissions, type of station (802.11b/g/n or802.11a), packet loss, jitter, and delay.

Examples of parameters measured per-channel are: total occupied aircapacity (from all sources) and WLAN air capacity, i.e. uplink,downlink, and total WLAN in the specific channel; the number ofstreaming sessions; the rate of each session; throughput of eachsession; and amount of packet loss.

The network parameters are measured on an on going basis, optionally inorder to calculate when it is possible or impossible to receive anadditional station into the network. The monitored parameters arecompared to the appropriate thresholds. In cases where it is possible toreceive an additional station into the network—the station is handledaccording to methods known in the art. In cases where it is not possibleto receive an additional station into the network—the maximum number ofsessions restriction method of the present invention is applied.Generally stated, from a systems perspective, it is always preferable todisconnect the most problematic station.

Calculating streaming performance quality. Preferably, Performancequality is calculated per station, average per channel, and/or as achannel saturation indicator.

An optional streaming quality measurement for per-station calculation ina VoIP application is the known in the art “R-value”. R-value measuresthe streaming session for packet loss, delay, jitter, and type ofvocoder. The output of the R-value is a quality measurement of thestreaming session.

The streaming performance quality may be Average per channel. This is acalculated average for each channel. For example, averaging thecalculated R value of all stations and comparing it to a threshold

The following are optional alternative streaming quality measurementsfor calculating when a streaming channel is saturated.

Calculating the average streaming quality of all stations and checkingif it is below a threshold. It is to be noted that checking if somethingis below or above a threshold are equivalent tests.

Calculating the percentage of stations whose streaming quality is belowa predefined threshold. This calculation focuses on specific stationsrather than the channel average.

Detecting saturation for a minimum predefined period of time. In thiscase, if a quality problem is fixed within a predefined timelimit—nothing is done. Optionally, if the problem is because a newstation was added to the network—the predefined time threshold may beshorter in order to prevent the network from becoming saturated.

Estimating channel saturation according to channel measurements. Thischannel calculation may be calculated in addition to or instead of theprevious station-based calculations. A main benefit of thischannel-based calculation is that the channel avoids being saturated byrestricting the number of stations it accepts. This is in contrast withthe station-based calculation wherein the channel accepts new stationsand then makes corrections such as disconnecting or moving stations.

It was found that there are cases where the jitter increases as thenetwork approaches saturation point 100. In an exemplary embodiment ofthe present invention, monitoring the jitter indicates when the networkis expected to reach saturation point 100. In this exemplary embodiment,the method of the present invention detects network overload based onthe amount of time a station waits before starting to transmit.

Estimating the channel capacity.

In the step of estimating the channel capacity, a value is calculated,based on the available data, for estimating how many streaming sessionscan be added to the channel. Examples of available data are networkmeasurements and the above described per-station and averagemeasurements.

In the case where the system operates a LB algorithm too, a station maybe forwarded to other channel. Therefore, the estimated channel capacityis calculated for all relevant channels and not only for the currentchannel (in order to know if it is possible to forward the station toanother channel).

In the case where the estimated channel capacity indicates that no moresessions may be added to the channel, and it is not possible to movesessions to another channel, the network does not accept any moresessions. Alternatively phrasing, estimating the channel capacity isequivalent to calculating the value of saturation point 100. The mainparameters affecting saturation point 100 are explained above.

Referring to FIG. 17, the QoS, as a function of the number ofsimultaneous sessions, is calculated dynamically, and/or measured byparameters such as jitter, packet loss and delay measurements. Streamingsaturation point 100 represents the maximum capacity of the network as afunction of the required sessions mixture and type of applications. Itis to be understood that the algorithms of the present invention takeinto account at least one of the aforementioned parameters affecting thelocation of saturation point 100. When the network is saturated, thevalue of all aforementioned parameters is reduced. Therefore, in anexemplary embodiment of the present invention, thresholds are placedover all parameters affecting the location of saturation point 100. Whenone parameter exceeds the threshold, the maximum number of sessionsrestriction algorithm is applied. Known in the art methods may be usedoffline for calculating and/or calibrating the threshold of eachparameter. Optionally, the thresholds are changed online. Thresholdsthat change online are especially useful for systems that are calibratedin the field. The calibration methods are known in the art of computernetworks and data communication.

Preferably, the current dynamic maximum possible number of sessionscalculation is performed periodically or immediately after loadbalancing and/or a disconnecting action and/or termination of anexisting session has been performed. It is to be understood that thedynamic maximum possible number of sessions threshold is a dynamicthreshold that depends on the state of the network. The calculations inthis step and the successive steps are repeated to prevent degradationof the system's performance. In an embodiment of the present invention,the maximum number of sessions restriction mechanism is run in the APsor in the access controller.

Managing the network's sessions. As detailed below, the sessions managermay (a) Limit the number of simultaneous sessions in the system in orderto prevent a decrease in the QoS. (b) Limit stations' data throughput.(c) LB stations.

It is to be understood that most descriptions and examples of thepresent invention relate to controlling the number of simultaneoussessions, but there is no intent to limit the scope of the presentinvention to number of sessions restriction. For example, the presentinvention may, alternatively or additionally, control the number ofstations connected to the network simultaneously and/or control thethroughput of the stations.

Optionally, the sessions manager load balances the network. LB may beglobal (between APs) or local (between channels of the same AP). Thefollowing are three optional preferred load balancing activities.

The first optional load balancing activity is moving (also known asroaming/handovering) and/or disconnecting new or existing stationswhenever the number of simultaneous sessions exceeds a threshold.

The second optional load balancing activity is identifying a networksaturation when a new session is initialized and performing one of thefollowing steps.

Disconnecting the session of the new station.

LB the new station to another channel or another AP.

LB another station or stations to another channel or another AP.

The third optional load balancing activity is identifying saturation dueto a change in a channel. Possible reasons for a change in a channelare:

The environmental conditions change and/or external interference wasadded. The interference may be wireless LAN interference or non-WLANinterference.

External interference of stations located in the area of interest of thenetwork and/or other interference sources.

The distribution/physical-location of the stations within the area ofinterest changes. It is to be noted that in some cases, one station'smovement is enough for blocking the transmission path.

Optional solutions for identifying saturation because of a change in achannel are:

Disconnecting the session of a specific station according to thealgorithm result. If the performance of a specific station wasdegraded—optionally move the station.

LB a station to another channel or AP.

Disconnect the station.

The following examples are cases where using LB results in a significantperformance improvement.

Separation between different types of stations, for example, separatingbetween 802.11g stations and 802.11b/g stations.

Separation between streaming and data stations. There are cases wherestations transmit both streaming and data, in that case the station mayreduce its data traffic rate.

Separating nearby and far away stations. Nearby stations usually havebetter performance than far stations that usually reduce the totalperformance of the channel. Separating nearby and far away stations isalso useful for dealing with the “capture effect” in which a nearbystation overrides a far away station.

Eliminating the hidden station problem by separating groups of stationsthat receive each other. Optionally, eliminating the hidden stationproblem is based on DOA.

Alternatively, the sessions manager disconnects stations.

Whenever the number of simultaneous sessions exceeds a maximum number ofsimultaneous sessions, new stations and/or existing stations aredisconnected. As known in the art, the most common optional stationdisconnection actions are: signaling disconnection, streamingdisconnection, wireless disassociation/disconnecting, and not acceptingnew sessions.

As disclosed above, the maximum number of sessions restriction mechanismof the present invention may, in some cases, disconnect a session.Herein disclosed are four optional methods for disconnecting a sessionin an IEEE 802.11 type of protocol: (a) Returning, at the state ofinitiating the session, a negative signaling response. Optionally, thenegative signaling response delivers a “network busy” message. (b)Ending the session by not passing the signaling packets and/or the voicepackets. (c) Disassociation of the station.

The following examples illustrate how highly useful it is to disconnector, alternatively, not accept stations.

Accepting only a predefined type of stations, for example, accepting802.11g stations and not accepting 802.11b stations.

Accepting only streaming stations and rejecting data stations. In thecase where a streaming station connects to the network while a datastation is transmitting, the session manager may disconnect the datastation in order to provide service to the streaming station.

Accepting nearby stations and rejecting far away stations.

Eliminating the hidden station problem by only accepting stations thatreceive the other stations. This can optionally be based on DOA.

Alternatively, the sessions manager disconnects stations having qualitybelow a threshold and/or interfering and causing performance degradationto other stations. In this case, the network is not saturated but thereis at least one station that is below the threshold—and this station isdisconnected.

Optionally, if the AP operates only one channel, it may be possible toLB the station to another AP or disconnect it.

Alternatively, if the AP operates more than one channel, it may bepossible to LB the station to another AP, or to another channel, or todisconnect it.

Optionally, connecting the system of the present invention to astreaming data information system.

To verify whether there is enough bandwidth to receive a new stationinto the network, a protocol for connecting the network of the presentinvention to a streaming data information system can be added to thepresent invention. The protocol for connecting the network of thepresent invention to a streaming data information system may supply thefollowing responses: (a) Enough bandwidth is available and the stationcan be connected to the network. (b) Not enough bandwidth is availableand the station cannot be connected to the network. (c) The stationshould be forwarded to another channel; On the other channel, thestation may be connected to the network.

Optionally, reducing the bandwidth of stations transmitting data whenthere are stations who need the bandwidth for streaming sessions.

In the case, when a first AP handles a streaming session that isdisturbed by transmissions of a data station and/or low prioritystation, the transmission power of the data station may be reduced inorder to reduce the interference with the streaming session operated bythe first AP.

Problematic Station Detection

FIG. 18 illustrates an embodiment of the present invention formonitoring a channel. According to FIG. 18, monitoring a channel isperformed as follows. It is to be understood that FIG. 1 is an exemplaryimplementation of the general concept of the present invention whichfeatures the following inputs: collecting statistics at all levels, peruser and per channel; and the following outputs: a decision todisconnect or LB a user.

Collecting raw traffic data 46 from one or more of the channels, APs,Ethernet, and/or bridging 14 device [add bridge 14 to fig].

Referring to FIG. 1, raw traffic data 46 is collected by collector 41.Raw traffic data 46, collected by collector 41, is used by SM and LBalgorithms. Raw traffic data 46 is collected on both the receiving andtransmitting directions and on the different channels/APs.

Optionally, sorting raw traffic data 46 by stations.

In an embodiment of the present invention, collector 41 sorts rawtraffic data 46 by stations.

Optionally, extracting statistical traffic data 47 from collected rawtraffic data 46 and control packets, which are sent to and received fromthe various stations.

Optionally, statistical traffic data 47 is extracted from collected rawtraffic data 46 and from control packets sent to and received from thevarious stations. Exemplary statistical traffic data 47 accumulated bycollector 41 includes at least one of the following:

(a) Packet statistics, including packet size, packet bit rate,retransmission counters, frame retransmission failure, etc.

(b) Recognition of VoIP or Video, or general streaming activityperformed by a station.

Application type. For example, TCP/UDP

(c) Packet classification performed by a designated classifier.Referring to FIG. 1, the classification is implemented by classifier 42.

(d) Reception level and quality of the link between MAP 11 and astation.

User profile, such as SLA.

Throughput per station.

Optionally, statistics are collected from the APs and stations usingIEEE 802.11k

Estimating the channel properties according to channel measurements.

This channel calculation may be calculated in addition to, or insteadof, the previous user-based calculations. The channel properties are afunction of the measured WLAN activities (i.e. any WLAN activity that isreceived in that channel) and other non-WLAN interferences received.

Extracting statistical information 48 from the collected raw trafficdata 46.

In an embodiment of the present invention, the channel is analyzed byanalyzer 40. Analyzer 40 extracts averages and high-level statistics 48from collected raw traffic data 46.

Local management algorithm 44 making decisions based on extractedstatistical information 48.

In an embodiment of the present invention, local management algorithm 44receives the collected and/or analyzed data; and based on theinformation it contains, decides what to do in the following exemplarycases:

Should the network be optimized?

Which stations should be handovered between channels, between APs, andbetween MAPs?

Should a station be accepted or disconnected?

How should stations be handovered?

Should the RF characteristics of the system be changed?

In an embodiment of the present invention, averages and higher-levelstatistics 48 are forwarded to global management algorithms as well.

Executing the decisions taken by local management algorithm 44.

In an embodiment of the present invention, the decisions made by localmanagement algorithm 44 are executed by executor 43. Executor 43 isresponsible for executing the policy decided by the SM and LBalgorithms. Executor 43 sends at least one command 50 to appropriate APs12A-C.

In an exemplary IEEE 802.11 type of protocol embodiment, executor 43 isthe component that receives from the algorithms the command todisconnect/roam a user, and executes the command. Moreover, based on thepolicy provided by the algorithms, executor 43 may decide whether toanswer a probe of a station and/or to accept association of a specificstation.

Referring now to the problematic station detection algorithm,

This algorithm searches for specific users that significantly degradethe whole system performance. Moving those users thus increases thetotal throughput of the system. A novel aspect of the present inventionis that the most interfering stations (i.e. stations that causeperformance degradation in relation to other users) are moved ordisconnected from the current channel. The decision is mainly madeaccording to the time that is wasted by a specific station compared toother stations and according to additional statistics. This is incontrast to prior art methods that simply separate users according totheir rate.

In an IEEE 802.11 type of protocol, problematic stations may severelydegrade the network's performance. In order to prevent the performancedegradation, the problematic station detection algorithm of the presentinvention is executed. Optionally, the problematic station detectionalgorithm is based on calculating the amount of time a station iswasting, but it is to be understood that calculating the amount of timea station is wasting is only an exemplary embodiment of the generalmethod of the present invention. Examples of additional/alternativeparameters that the problematic station detection algorithm may be basedon are:

The amount of network resource waste caused by the specific station,i.e. how much system resources are wasted because of a specific station.For example, a hidden station causes many collisions, and thereforewastes a large amount of network resources.

Another example is a station having a limited RSSI, which thereforeneeds many retransmissions at a low rate.

Calculating the amount of time that is wasted by a specific station.

The term “station-wasted time” is defined herein as the time used by astation for transmitting without receiving an acknowledge signal (ACK).Similarly, the term “network-wasted time” is the sum total of allstations' wasted time.

In an embodiment of the present invention, the wasted time is calculatedby summing the time of all retransmissions for which the station did notreceived an ACK. Preferably, the time for each retransmission for whichthe station did not received an ACK is equal to the packet'stransmission time plus the time wasted on waiting for receiving the ACK.The waiting time starts immediately after the end of the transmission.This waiting time is known as “ACK time out” in IEEE 802.11 type ofprotocol. Optionally, calculating the wasted time on the downlinkchannel is different from calculating the wasted time on the uplinkchannel.

Referring to calculating the wasted time on the downlink channel, theexact number of retransmissions and each retransmission's rate areknown. Therefore, the wasted time calculation is a straightforwardprocess.

Referring to calculating the wasted time on the uplink channel, theexact number of retransmissions and each retransmission's rate are notknown, and more specifically, in the uplink channel what is only knownis whether or not there was a retransmission. Therefore, the wasted timecalculation is based on estimating the relevant paraments.

Another optional input to the algorithm is the amount and type oftransmitted data. For example, if a station transmits more data comparedto other stations, than its wasted time is probably longer, but itsrelative percentage of wasted time is lower. The algorithm should takesinto account this difference when deciding which station to disconnector LB.

Alternatively, a proprietary protocol is used for obtaining a betterestimation of the time being wasted by a station. Exemplary additionalinformation used by the proprietary protocol are: (a) the number ofretransmissions, (b) hidden station indication, (c) transmissions rates.

An example of a proprietary protocol that supplies additionalinformation about the measurements is the IEEE 802.11k.

Comparing the amount of time wasted by a specific station with theamount of network time wasted by all stations, on average.

The average amount of network time wasted by all stations is calculatedby summing up the wasted transmissions times of all the relevantstations and dividing the result by the total number of relevantstations.

Identifying a specific station as a problematic station if the amount oftime that the station wastes is more than the average amount of timewasted in the network, plus a factor.

In an embodiment of the present invention, a low-pass filter is operatedon the measurements in order to filter out the random noises andnon-representative problems.

The factor that is added to the amount of time wasted in the network maybe predefined or set dynamically.

Optionally, the algorithm takes into account the amount and type oftransmitted data. For example, if a station transmits more data comparedto other stations, than its wasted time is probably longer, but itsrelative percentage of wasted time is lower. The algorithm should takesinto account this difference when deciding which station to disconnector LB.

Optionally, moving a problematic station to another channel/AP ordisassociation.

The novel problematic-station-detection algorithm of the presentinvention may significantly increase the total throughput of a network.In specific scenarios, the throughput may be multiplied by 10 due to theabove-disclosed problematic-station-detection algorithm.

The discussed algorithm of the present invention may be further improvedby applying the following, optional steps.

Optionally, assigning a minimum received threshold to respond to in eachspecific channel.

When an AP receives from a station signals which are below a minimumreceived threshold, the AP may not respond. This is done by assigning aminimum answering-threshold to the transmissions received on eachspecific channel.

This method prevents a situation wherein a station connects to thenetwork, interferes with the network, is identified by the algorithm,but until it is moved—degrades the network performance. This method doesnot allow a problematic user to connect to the network and thereforeprevents the performance degradation ahead of time.

The steps for identifying problematic users in this case are:

Measure the RSSI of all stations

Measure the performance/throughput of the whole channel

Estimate the minimum RSSI level of a new user below which it isestimated that the new station might degrade the total performance.Optionally, the estimation assumes that there is another channel thatcan accept all users.

Receive a user's probe request and/or association request, and respondpositively only if the measured RSSI of the user is above the minimumthreshold.

Optionally, assigning specific stations having high QoS requirements, toa specific channel.

In an embodiment of the present invention, at least one channel isreserved for stations that are specifically sensitive to QoS issues,such as VoIP and Video over IP applications. The communication networkof the present invention ensures that those reserved channels featurethe required QoS by assigning a specific channel for sensitiveapplications. Whenever the specific channel for sensitive applicationsgets close to reaching its saturation point, additional stations aredirected to other channels, or even to other APs.

Optionally, problematic-station-detection algorithms are run in GlobalManagement 17 when the stations are moved between APs controlled bydifferent problematic-station-detection algorithms. In this case,problematic-station-detection algorithms can be referred to as SMalgorithms.

[Using Problematic-Station-Detection Algorithm to LB and SM]

Referring now back to the LB algorithm of the present invention, whentwo stations transmit at the same time there is a collision. Anotherpossible scenario for a collision occurs when a first station istransmitting, and a second station that does not receive thetransmissions of the first station, transmits to the same AP. In thiscase, a collision occurs and the AP may receive only one transmission,or none. In order to solve this problem, a station which does notreceive the transmissions of another station can be notified by the APto expect a transmission, and not to transmit. An alternative solutionis to make sure that closely located stations are transmitting on thesame channel, and therefore receiving the transmissions of one another,and are not transmitting when transmissions from another station arereceived by them. Problematic-station-detection algorithms are run inthe APs when the stations are moved between different channels, i.e.between different APs controlled by the sameproblematic-station-detection algorithm. In this case, theproblematic-station-detection algorithms can be referred to as LBalgorithms.

Additional criteria and methods for moving stations between APs andbetween channels on the same AP.

In an embodiment option of the present invention, Access Control 22builds a map that includes the following information:

All APs

All stations

Which AP is receiving which station

At what power each station is received by the appropriate AP.

According to the map, a decision regarding whether to force a station topass to a different MAP and/or to a different channel, i.e. differentAP, is reached.

A significant and particular aspect of the novelty and inventiveness ofthe present invention, relating to the map built in Access Control 22,is that it enables the MAP to move stations between channels and betweenMAPs. Moving stations between channels and between MAPs may hereinsometimes be referred to as “soft force roaming” and sometimes as “hardforce roaming”. Moving the station may be between one AP and another APor a specific channel in the other AP, depending on each channel's load.

In prior art IEEE 802.11 systems types, the station decides whether totransfer to a different AP or channel. Using the map helps the MAPoperate the soft force roaming and hard force roaming.

In an embodiment of the present invention, in order to move stationsbetween channels and between MAPs, the system limits both the minimumlevel of reception sensitivity, as well as the minimum level ofreception sensitivity to which it is replying to probe transmissionsfrom a station. On the fastest channel, responses are made only to astation that meets specific criteria. For example, the system does notrespond to IEEE 802.11b station types on channels which are allocated toIEEE 802.11g station types. Moreover, the system ensures that eachstation type (IEEE 802.11b and IEEE 802.11g) is connected to itsappropriate channel.

It is to be understood that a problematic station detection algorithmmay detect multiple problematic stations in serial or parallel.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination.

It is to be understood that the present invention is not limited in itsapplication to the details of the order or sequence of steps ofoperation or implementation, nor to the details of construction,arrangement, and composition of the corresponding thereof, set in thedescription, drawings, or examples of the present invention.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention.

While the invention has been described in conjunction with specificembodiments and examples thereof, it is to be understood that they havebeen presented by way of example, and not limitation. Moreover, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art. Accordingly, it is intended toembrace all such alternatives, modifications and variations that fallwithin the spirit and broad scope of the appended claims and theirequivalents.

1. A method for spectrum-management of wireless stations comprisingaccess points that transmit directionally and assigning a predefinedchannel in a predefined direction, in order to reduce interferencebetween closely located access-points.
 2. The method of claim 1, furthercomprising placing a null in the direction of said interference.
 3. Themethod of claim 1, wherein the spectrum-management algorithm is rundistributed.
 4. The method of claim 1, wherein the spectrum-managementalgorithm is run centralized.
 5. A method for spectrum-management ofwireless stations comprising: (a) determining an overlapping areabetween at least two access-points, and (b) placing a dynamic null inthe direction of said overlapping area by using a smart antenna.
 6. Amethod for spectrum-management of wireless stations comprising: (a)mapping stations experiencing interference and the direction of saidinterference, and (b) dynamically assigning channels featuring highinterference to stations featuring high interference, and dynamicallyassigning channels featuring low interference to stations featuring lowinterference.
 7. The method of claim 6, further comprising the step ofload balancing at least one of said wireless stations according to themapped interference.
 8. A method for operating nearby 802.11 type ofprotocol access-points, comprising: (a) transmitting directionally fromsaid access-points by using a smart antenna, (b) mapping the availablestations, and (c) distributing said available stations between saidaccess-points.
 9. The method of claim 8, wherein each of said availablestations receives signals only from one of said access-points.